RUMINANTS

Abortion caused by Helicobacter trogontum in a sheep flock

Maria Spinato, Margaret Stalker, Durda Slavic, John McNally

A producer with a flock of 250 Bluefaced Leicester and Scottish Blackface sheep reported 3 abortions of near-term fetuses in a group of 52 breeding ewes. This group of crossbred ewes had been recently purchased and relocated from Saskatchewan. Two additional abortions had occurred previously; however, fetuses were at an earlier stage of gestation, and diagnostic testing was not pursued. Ewes appeared to be healthy, in good body condition, and had been recently vaccinated and dewormed. The ration consisted of corn silage, oats, and free-choice hay. Samples of fresh placenta obtained from two abortions were submitted to the AHL for testing.

Cotyledons in one placenta were noted to be mildly swollen. Samples of placenta were submitted for culture for common bacterial pathogens including Campylobacter spp., PCR testing for Coxiella and Chlamydia, and histologic examination. No significant bacterial pathogens were isolated in culture, and PCR tests for Coxiella and Chlamydia were negative. Histologic features in both placentas were similar: autolysis was moderately advanced and trophoblastic epithelium was sloughed. Extensive infiltrates of neutrophils were present within both cotyledonary and intercotyledonary chorioallantois (Fig. 1). In one placenta, several allantoic arterioles were undergoing leukocytoclastic vasculitis, associated with occasional thrombosis. Based upon the histologic findings of marked suppurative placentitis, further testing for infectious causes of ovine abortion was initiated. PCR testing for Toxoplasma and Leptospira was negative, and immunohistochemical staining for BVDV/Border disease virus was also negative.

Reports in the literature of sporadic cases of ovine abortion caused by Flexispira rappini in New Zealand and the United States caused us to pursue further PCR testing of saved frozen portions of placenta using genus-specific Helicobacter primers. The obtained PCR product was sequenced, and sequence results (100% coverage and 99.4% identity) revealed the presence of Helicobacter trogontum, previously known as Helicobacter (Flexispira) rappini. Additionally, immunohistochemical staining of the placental lesions using rabbit anti-H. pylori polyclonal antibodies (Dako) revealed widespread positive immunostaining (note: previous literature reports have described cross-reactivity of this antiserum with multiple Helicobacter species) (Fig. 2).

A recent retrospective diagnostic survey of laboratory submissions from ovine abortion outbreaks in New Zealand (NZ) identified Helicobacter bilis and Helicobacter trogontum as causes of late-term abortions in a small, but significant proportion of affected flocks. In the NZ outbreaks, postmortem and histologic lesions in affected fetal livers resembled those of Campylobacter spp., consisting of hepatomegaly and multifocal hepatic necrosis. Large curved bacilli situated within viable hepatocytes bordering necrotic foci were visualized by positive Warthin-Starry silver staining. The authors described one case that was positive for Helicobacter spp. by PCR and that lacked hepatic lesions. Placentas were not available for examination.

This is the first identification by the AHL of Helicobacter trogontum as a cause of placentitis and abortion in sheep. Whether this organism is a sporadic, previously undetected or emerging cause of infectious ovine abortion in Ontario remains to be elucidated. Much remains unknown regarding the source of the organism, the method of transmission and its pathogenicity. Molecular tools have now provided us with the means of answering some of these questions.   AHL

Reference

Gill J, et al. Helicobacter bilis and Helicobacter trogontum: infectious causes of abortion in sheep. J Vet Diagn Invest 2016;28:225-234.

Figure 1. Autolysed chorioallantois infiltrated by neutrophils.

Figure 2. Positive IHC staining for Helicobacter spp. in ovine placenta.

Complex vertebral malformation syndrome in a full-term Holstein fetus

Heindrich Snyman, Henry Ceelen

A single full-term, fully haired, aborted Holstein fetus, and its associated placenta and attached umbilical cord was received by the AHL-Kemptville for postmortem evaluation. The fetus originated from a heifer that had reached her due date but had failed to show any premonitory signs of calving. The dam was subsequently induced (10 mL dexamethasone, 3 mL cloprostenol) but failed to progress and the dead fetus was ultimately delivered via caesarian section.

At postmortem there was marked shortening of the neck, and the cervical profile was irregular (Fig. 1). The cranial-to-caudal thoracic vertebral column was similarly irregular and had moderate scoliosis. All 4 limbs were fixed with arthrogryposis (Fig. 1). The head was smaller than expected with subtle rostro-caudal shortening, doming, and incomplete coverage of the caudal cranial sutures forming and ~ 2.0 x 1.6 cm retained inter-sutural space. There was no herniation or extension of meninges or brain from this site. Upon opening the calvaria, the brain was very soft and collapsed on removal (suspect hydrocephalus). The vertebral column was split mid-sagittally to evaluate the vertebral bodies. Within the cervical vertebral column, vertebral bodies C3 to C7 were irregular, small and angular-to-wedge-shaped and there was partial fusion of the C5/C6 vertebrae (Fig. 2). Similar shortening and irregularity was observed within the T1 to T5 thoracic vertebrae, but changes were less obvious than for the cervical vertebrae. The ribs and sternum as well as the lumbar and sacral vertebrae appeared grossly unremarkable. The heart was globose and flaccid with biventricular dilation and a 1.2-cm ventricular septal defect ~1 cm below the aortic semilunar valves (Fig. 3). The lungs were not inflated and there was mild associated pulmonary congestion and edema. The changes noted in the cervical and thoracic vertebral column, head, and heart are characteristic of complex vertebral malformation (CVM). In addition, both the dam and sire were known carriers for CVM. With the assistance of Holstein Canada, samples of fetal skeletal muscle was sent for genetic testing and the fetus was found to be “CVM affected”.

CVM is a congenital autosomal recessively inherited disorder of Holstein cattle resulting from a single base missense substitution in the nucleotide sugar transporter gene SLC35A3. It has been traced back to the US Holstein sire Penstate Ivanhoe Star and one of his sons Carlin-M Ivanhoe Bell and their offspring, and represents the single most prevalent inherited disorder in Holstein cattle. CVM-affected fetuses are aborted ~75% of the time with the remaining ~25% usually terminating in stillbirths. The SLC35A3 transporter plays a significant role in NOTCH signalling and the formation of the vertebral column during embryonic development and differentiation of the unsegmented paraxial mesoderm. As a result, this syndrome is associated with significant cervical and thoracic vertebral malformation, malformed ribs, and arthrogryposis. Additionally, cardiac anomalies are also often reported (including septal defects, great vessel malformation, and myocardial hypertrophy).   AHL

References

Agerholm JS, et al. Complex vertebral malformation in Holstein calves. J Vet Diagn Invest 2001;13:283-289.

Thomsen B, et al. A missense mutation in the bovine SLC35A3 gene, encoding a UDP-N-acetylglucosamine transporter, causes complex vertebral malformation. Genome Res 2006;16:97-105.

Figure 1. Aborted Holstein fetus with irregular and shortened neck and arthrogryposis.

Figure 2. Mid-sagittal split vertebral column with irregular wedge-shaped C3-C7 cervical vertebral bodies (arrows) and partial fusion of the C5/C6 vertebrae (asterisk).

Figure 3. Heart with high ventricular septal defect (arrow).